The present invention relates to detergents based on salts of alkyaryl sulfonic acids. The alkyl groups are highly branched, which provides superior performance in drive-line applications such as automatic transmission fluids.
In automatic transmission fluid applications, branched chain sulfonates, typically derived from polypropylene-alkylated benzenes, are widely used, as they tend to impart stable dynamic frictional properties to formulations in which they are incorporated. Less expensive and more readily available linear sulfonates, derived from polyethylene alkylates, tend to give dynamic friction values which are unacceptably low for most automatic transmission applications.
Much effort has gone into formulating lubricants for drive-line applications. U.S. Patent Application 2004/0102339, Aoyagi et al., May 27, 2004, discloses a method for improving the frictional properties of functional fluids, e.g. the brake and clutch capacity. The friction-modifying material is a polyalkenyl sulfonate or alkali or alkaline earth metal salt, derived from a mixture of polyalkylenes comprising greater than about 20 mole percent alkyl vinylidene and 1,1-dialkyl isomers. The material is useful in automatic transmissions. Examples: methyl vinylidene isomer and 1,1-dimethyl isomers. Preferred monoolefins include propylene, butylene, particularly isobutylene, 1-octene and 1-decene. Polyolefins include, among others, polybutene, including polyisobutene. The polyisobutene sulfonates provide high frictional properties, as measured by Komatsu micro-clutch friction test (friction coefficient)
U.S. Patent Application 2004/0209787, Aoyagi et al., Oct. 21, 2004, discloses a method of improving the brake and clutch capacity of a functional fluid, comprising adding a friction-modifying amount of a polyalkenyl sulfonate.
U.S. Pat. No. 6,551,967, King et al., Apr. 22, 2003 discloses low overbased alkylaryl sulfonates. The alkyl group is a C15-C21 branched chain alkyl group derived from a propylene oligomer. An alkylbenzene is prepared by reacting a propylene oligomer with benzene. The propylene oligomers have an average of about 15-21 carbon atoms and a low di-olefin content.
U.S. Pat. No. 6,410,491, Harrison et al., Jun. 25, 2002, discloses a polyalkenyl sulfonic acid composition derived from a mixture of polyalkenes comprising greater than 20 mole percent alkyl vinylidene and 1,1-dialkyl isomers. In a preferred embodiment, the polyalkene is polyisobutene.
PCT Application WO 95/17489, Watts et al., Jun. 23, 1995, discloses a method of increasing the static coefficient of friction of an oleaginous composition such as an ATF, by adding a product of an oil-soluble substituted or unsubstituted, saturated or unsaturated, branched hydrocarbyl group containing from about 12 to about 50 total carbon atoms; a linking group; and a nitrogen-containing polar group.
There are many other patents and patent applications which describe lubricant formulations suitable for automatic transmissions. One among these many is U.S. Application 2006-0172899, Tipton et al., Aug. 3, 2006.
It would be desirable to be able to select alkylated or hydrocarbyl-substituted aromatic materials for use in forming sulfonic acids, such that the drive-line fluid into which they may be included will have favorable and stable dynamic frictional properties. The present invention provides such materials.